Spark-plug tester



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Patented Aug. 13, 1929.

UNITED STATES PATENT OFFICE.

RALPH E. HANTZSGH, OF EAST ORANGE, NEW JERSEY, ASSIGNOR OF ONE-HALF TO DALLAS R; LAMONT, OF BROOKLYN, NEW YORK.

SPARK-PLUG TESTER.

Application filed January 18, 1922, Serial The present invention relates to apparatus for indicating the occurrence of an electric spark between adjacent electrically conducting elements, and is designed particularly for use with internal combustion engines to indicate whether a proper spark is present within the engine cylinder and is occurring with proper regularity.

The universal practice in the manufacture of internal combustion engines is to equip each of the engine cylinders with a removable element or spark plug having connections leading to the electric generator which furnishes ignition current for the en gine carrying at its end which lies within the cylinder a pair of electrical conductors extending into closely adjacent relation. The generator with its associated timing mechanism is arranged to periodically cre-.

ate, in synchronisni with the rotation of the engine, a difference of potential between these adjacent conductors. The result is that every time the engine piston has compressed a combustible mixture of fuel and air within the cylinder a spark discharge occurs and effects a rapid combustion or explosion of the mixture, the expansive force of the explosion serving to impel the piston on its working stroke along the length of the cylinder.

A frequent cause of irregularity in operation of internal combustion engines is the failure to obtain a proper ignition spark within the cylinder. Due to the extremely high temperatures and generally adverse conditions to which the spark plug conductors are subjected within the cylinder, deposits of dirt and carbon are likely to form on them and impair the character of the spark or even build up sufliciently to completely bridge the gap between the conductors and permit current to pass with no spark discharge whatever, thus preventing ignition of the combustible mixture in the On the otherhand, the gap between the spark plug terminals within the cylinder may be too great to permit discharge of a spark, due to the improper setting of the gap in the factory or to accident during shipment or during the process of fitting the plug into the cylinder, or a drop of oil or other insulating material may collect on the end of one of the conductors and effectually prevent thepassage of a spark No. 530,023. Renewed January 17, 1929.

across the gap. lt-is, therefore, desirable that some means be provided for indicating whether a proper spark discharge s obtained, particularly in the case of automobile engines which are often in the care of inexperienced operators and which are frethe engine and to note whether a spark is obtained. It has also been proposed to provide indicating means such as, for instance, a partially evacuated tube having one contact held by the operator on the high potential terminal of the spark plug, the presence ofthe high potential causing ionization of the rarefied gas within the tube which is indicated by a glow of color depending upon what gas is present in the tube. These methods, are, however, open to the objection that the indication isin no way dependent upon the actual occurrence of a spark discharge but depends upon the presence of a potential difference between the terminals of the spark plug. By either of the above methods, for instance, the spark gap may become oil insulated or too wide for the passage of a spark and the indication obtained by the test would nevertheless show the spark to be occurring properly because there is a proper potential diiference existing between the spark plug terminals. It has further. been proposed to employ a second gap in series with the spark plug and located in a position to be readily observed. However, inasmuch as such a gap is in series with the spark plug gap at all times, it is objecti0nable due to the fact that it lowers the voltage available for effecting a spark discharge within the cylinder and impairs the quality of the spark obtained.

It is accordingly a principal object of the invention to provide an apparatus for testing spark plugs in which the indications ob tained depend on the actual discharge of a spark between the terminals of the spark plug, and the indications of which are consequently dependable as showing whether a spark within the cylinder is obtained.

' It is also an object to provide an apparatus of this type which indicates whether the spark is occurring in a vigorous manner and with the proper regularity.

It is a still further object to provide an apparatus of this type in a convenient form of small dimensions and rugged construction which may be manufactured at a cost sufiiciently low to render. it readily saleableto individuals, and which may be used by inexperienced persons without danger to the user or likelihood of obtaining erroneous indications.

I have illustrated a preferred embodiment of my invention in the accompanying drawings, in which Figure 1 is a longitudinal sectional view showing my improved spark plug tester applied to the terminals of a spark plug; Fig 2 is a plan view; Fig. 3 1s a longitudinal sectional view showing a mod fied construction; Figs. 4 and 5 are longitudinal sectional views showing further modifications; Fig. 6 is a view illustrating a tester of the type shown in Figs. 4 and 5 applied to the spark plug; and Figure 7 1s a View showing a detail.

Referring to Fig. 1 of the drawings, 1 indicates'an enclosing housing within which the parts of the apparatus are contained.

, This housing may be of any desired material,

preferably non-conducting, and is here shown of substantially cylindrical shape. Positionedwithin the housing 1 is a (301i 2 preferably of such dimensions that its outside diameter -is substantially equal to the inner diameter of the housing. A second coil 3 containing a fewernumber of turns is located within the coil 2 and may be held in place in any desired manner, an 1nsulating sleeveor member 4 being provided. between the two coils and a second insulating sleeve 5 fitted within the coil 3, if desired.

- In the central space within the housing 1 is located a condenser 6 of any desired construction but which may conveniently be formed of two sheets of tin foil or similar electrically conducting material separated by a sheet of appropriate insulating material, and the whole rolled into a cylindrical form, as shown, of one or more turns as is necessary to furnish sufiicient capacity efi'ect. At one end of the housing 1 a spark gap is provided which may conveniently consist of a metallic screw 7. pointed at its end to facilitate proper location and discharge of the spark anda cooperating member 8 havinga widened surface adjacent the member 7 to receive the discharged spark. The

' member -7" m;a,y conveniently be threaded within the wall of the housing as indicated at .9 so that the length of the spark gap may be adjusted. The end of the housing may be left uncovered, if desired, but is preferably provided with a transparent covering 10 which permits the spark to be observed from the exterior of the housing and at the same time excludes dust and dirt from the working parts of the apparatus. Contacts l1 and 12 are provided at the exterior of the housing for engagement with the terminals of the spark plug and a handle 13 is attached to the housing for convenience in the use of the apparatus.

In the operation of an internal combustion engine a magneto or equivalent electrical generating device is employed to furnish the ignition spark, and such generator and its associated timing mechanism serve the purpose of periodically creating a potential difference between the terminals of the spark plug and efi'ecting the discharge of a spark across the gap 14 between the contacts 14 and 14 of the plug which lie within the engine cylinder. Accordingly, when the contacts 11 and 12 of the tester are applied to the terminals of the spark plug these contacts are subjected to the same potential difference which is present between the terminals of the plug. The contact 12 is connected through a lead 12 with one terminal of the condenser 6, the other terminal of the condenser being connected through a lead 3 to one end of the coil 3, the other end of which is connected to the contact 11 at 3 Thus, when the tester is applied to the spark plug, the circuit containing the coil 3 and condenser 6 is connected across the spark gap of the plug.

One end of the coil 2 is connected as shown at 2 to the terminal 7 of the spark gap provided on the tester, and its other end is connected by means of a lead 2 to the terminal 8 of this gap. If necessary or desirable a small condenser may be arranged in circuit with the coil, but the capacity effect between turns of the coil will ordinarily be sullicient. At the time a spark occurs between the terminals 14 and 14 of the spark plug, the condenser 6, which in series with the coil 3 is connected across the spark gap, has become charged to'a voltage substantially equal to that occurring across the terminals of the plug. When the actual discharge of a spark occurs across the gap 14, the condenser 6 discharges its stored quantity of electricity through the coil 3 and the spark gap 14 of the plug. The rapidly changing current occurring within the coil 3 induces a potential difference along the length of theassociated coil 2 which is in inductive relation with the coil 3. Inasmuch as theiterminals of the coil 2are in electrical connection with the members 7 and 8 of the spark gap provided on the tester, theinduced voltage within the coil 2 will cause the discharge of a spark between the terminals 7 and 8. This result may be obtained whenever two coils are arranged in inductive relation with each other. The most eflicient transfer of energy from one coil to the other occurs, however, when the natural frequency of the circuit containcontaining coil 2; that is, when the product of the inductance and capacity in one circuit is equal to the product of the inductance and capacity of the other. Inasmuch as the capacity in the latter circuit is ordinarily due entirely to the capacity effect occurring between turns of the coil 2, or this effectaugmented by the addition of a small condenser, the number of turns mustbe relatively great, and the desired natural frequency of the circuit may be obtained by merely winding into the coil 2 a sufiicient number of turns. his particularly to be noted that, inasmuch as the induced voltage within the coil 2 is directly dependent upon the discharge ofa spark between the terminals of the spark plug, no spark can occur between the terminals 7 and 8 of the tester unless a spark dischar e actually occurs be tween the terminals 0 the spark plug.

The particular arrangement of elements within the housing 1 as well as the type or form of these elements is subject to modification, as desired. For instance, in Fig. 3'1 have shown an embodiment of my invention in which the coil 3 is located at the end of the housing opposite the test gap, and in which the condenser consists of alternate sheets of conducting material and insulating material arranged one above the other in the bottom of the housing. It is obvious that by increasing the number of layers in the condenser, the magnitude of the capacity may be varied over a wide range without materially affecting the size of the apparatus. In-

asmuch as the conducting portions of the condenser 6' constitute closed conducting rings in inductive proximity to the coils 2 and 3, a small sector is preferably cut out of each of the conducting layers of the condenser, as shown in Fig. 7, for the purpose of reventing such layers exerting an undeslrable action on the transfer of energy between the coils. The adj acentends of the coils2 and 3 are here shown interconnected at 16 for the purpose of maintaining them at substantially the same potential and thus obviating any danger of a short circuit through the insulating medium 4.

The parts of the apparatus may be assembled within a housing of any desired shape. For instance, in Fig. 4 I have shown the housing 1 in substantially the shape of a pencil so that the apparatus may be readily carried about by the user in his pocket in the manner of a pen or pencil. In this embodiment the contact 12 is provided in the form of a metallic point inserted at the pointed end of the housing, while the contact 11 is in the form of a metallic ring surrounding the body of the housing and preferably broken at one point in its length to avoid many short circuiting effect on the coils of the is paratus due to inductive action. The conenser is here shown as constituted of a conducting ring 15 insertedwithin the housing and separated from the ring 11 by the insulating wall of the housing. The conduct ing elements 11 and 15 thus serve as the two plates of the condenser and are insulated by the wall of the housing lying between them. If suflicient capacity is not obtained with this arrangement it may be augmented by the addition of a small condenser of any desired type. It is, of course, understood that any of the described types of condensers may be employed as desired.

In this embodiment the terminals 7 and 8 of the test spark gap are enclosed within a spark discharge between terminals 7 and 8 no longer occurs, but that, due to the potential difference between these terminals, the rarefied gas Within the tube becomes ionized and the presence of the potential difference is indicated by a glowing within the tube. By introducing proper gases into the tube at low pressure a desired color of glow may be obtained. I have here shown the coil 3 positioned within the coil 2, it being understood that proper insulating mediums will be provided.

In applying a tester of the type shown in Fig. 4 to the spark plug the contact 12 at the tip of the housing is placed against the engine cylinder at a point near the base of the spark plug and the tester then tilted over in such position that the contact ring 11 will rest against the tip of the spark plug, as shown in Fig. 6. At every discharge of a spark within the engine cylinder a corresponding spark will be produced across the spark gap of the tester and may be viewed throu h the window 10.in the side of the housing. The contact ring 11 may conveniently be made of sufficient length to permit considerable variation in the position of the contact 12 against the engine frame and still cause the contact 11 to come into engagement with the top of the spark plug when the tester has been tilted into indicating position, and to further facilitate application of the tester to spark plugs of different height.

In Fig. v5 I have shown a still further arrangement of elements, the housing being of the same general shape as that shown in Fig.4. In this embodiment a single continuous coil is employed, the upper portion 2 constituting a greater number of turnsthan the lower portion 3. With this arrangement, and particularly when a condenser 6 of the cylindrical type is employed, the apparatus may be made extremely slender and made to closely resemble a pen or pencil if desired. The portions 2 and 3 are not in as closely coupled relation in this construction, but may be arranged to operate satisfactorily particularly if the natural frequencies of the two circuits are approximately the same. The condenser 6 consists of .a thin glass tube provided on the inside and outside with a layer of tin foil or other Suitable conducting material. This type of construction is convenient in manufacture and affords a compact and rugged element denser of considerable capacity, particularly if the glass of the tube be very thin. The indicating spark gap is here shown o.s1- tioned at the upper end of the housing and the terminal 7 thereof consists of a metallic rod extending longitudinally of the housing and serving as a conductor to which the terminal of the condenser 6 may be connected and also as a terminal for one end of the coil portion 2. I have shown one portion 2 of the coil connected into the circult comprising the test gap and the remainder of the coil connected in circuit with the condenser 6. If desired, however, I may connect the entire coil or any desired portion of it in circuit with the test gap, utilizing any desired number of the same or different coil turns for connection in circuit with the condenser 6 after the manner of an auto-transformer. It is to be understood, of course, that an indicating element of the type shown in Fig. 4 may be employed in lieu of thespark gap.

In the testing of a spark plug with my improved apparatus a spark will occur across the gap of the tester corresponding to each normal spark discharge between the terminals of the spark plug. In case the terminals of the plug have become dirty and carbonized so that a short circuit occurs and there is no spark being discharged within the engine cylinder, th'e indicating spark gap of the tester will not be actuated inasmuch as the condenser 6 cannot build up a voltage, it being short circuited through the carbonized gap 0 the plug. The absence of a spark bebvl een the terminals of the tester will thus indicate that no spark is being produced within the engine cylinder. In case the spark plug terminals within the engine cylinder have become partially covered with a deposit of dirt and carbon so that the spark is irregular or feeble, the induced voltage generated in the coil 2 of the tester upon discharge of a spark will not be sufiiciently great to cause a spark to occur at the indicating gap. The particular voltage at which the indicator will be actuated may be readily regulated by varying the length of the indicating gap as desired. In case the spark within the cylinder is intermittent or otherwise functioning irregularly, the spark at the indicating gap will occur with a corresponding irregularity and will indicate the true nature of the spark discharge which is actually occurring within the cylinder.

It frequently happens that the spark plug terminals within the cylinder are set too far apart fora discharge to occur or become bent into such position through accident. In such case, although a proper potential difference exists between the spark plug terminals, no discharge will occur across the gap on the tester. Likewise, if the points of the spark plug terminals become covered with oil and are thus effectually insulated from each other and prevent passage of a spark between them, the indicating gap on the tester is not actuated and thus shows that no spark is being obtained within the cylinder.

WVhile I have illustrated and described preferred embodiments of my invention, it is to be understood that certain changes such as the particular arrangement and type of elements employed, the nature of the indicating element used, and the like, may be varied within the full scope of the appended claims.

I claim:

1. A spark indicating system of the class described for indicating the occurrence of the ignition spark in the ignition system, comprising an electrical circuit containing inductance and capacity, a second circuit in inductive relation with said first circuit, means in said second circuit for indicating the presence of a predetermined potential difference therein, and means for connecting said first circuit across the spark plug wherein the spark being indicated occurs.

2. A spark indicating system of the class described for indicating the occurrence of the ignition spark in ignition systems, comprising an electrical circuit containing inductance and capacity, means for connecting said circuit across the ignition system spark gap, a second circuit in inductive relation with said first circuit, and indicating means associated with said second-circuit, actuated by the discharge of a spark across said gap.

3. Apparatus of the class described for accurately indicating the occurrence of the ignition spark at the spark gap of an ignition system, comprising an enclosing housing, a

coil within said housing, a condenser in circuit with said coil, conductors leading to the exterior of the housing for connection across the spark gap, a second coil within said llOllS- ing, and means associated with said second .coil for visibly indicating the discharge of a spark across the said gap.

4. A spark indicating system of the class described for ignition systems, comprising a circuit containing inductance and capacity, means for connecting said circuit to the terminals of the spark plug at which the ignition spark of the ignition system occurs, a second circuit containing inductance and capacity in inductive relation with said first circuit whereby oscillations are produced in said second circuit upon discharge of the ignition sparkbetween the terminals of the spark plug, and means within said second turns inductively associated with said first coil, and means associated with said second coil for indicating oscillations produced therein due to the discharge of a spark between the terminals of the spark plug.

6. Spark indicating apparatus of the class described for indicating the actual occur rence of the ignition spark in ignition systems, comprising an electrically conducting coil, a second coil within said first coil, means for connecting one of said coils in circuit with the spark gap at which the ignition spark occurs, and means in circuit with the other of said coils for indicating the discharge of a spark across, said gap.

7. Apparatus of the class described for testing the ignition spark of an ignition system, comprising an enclosing housing, a coil within said housing, a second coil within said first coil, a condenser in circuit with one of said coils, means for connecting said coil and condenser across the spark gap at which the ignition spark of the ignition system occurs, and means infcircuit with the other of said coils for indicating the discharge of a spark across said gap.

8. Apparatus for indicating the occurrence of a spark between the terminals of a spark plug of an ignition system, comprising an enclosing housing, a coil within said housing, a condenser in circuit with said coil, contacts at the exterior of the housing for application to the terminals of the spark plug, one of said contacts being of extended area, connections between said contacts and said coil and condenser within the housing, a second coil within said housing, and means for detecting oscillations produced therein due to the discharge of a spark between the terminals of the spark plug.

9. Apparatus for indicating the occurrence of a spark between the terminals of a spark plug of an ignition system, comprising an enclosing housingya coil within said housing, a condenser in circuit with said coil,

contacts at the exterior of the housing for application to the terminals of the spark plug at which the ignition spark occurs, one of said contacts being of appreciable width and substantially surrounding said housing, connections between said contacts and said coil and condenser within the housing, a second coil within said housing and means for indicating oscillations produced therein due to discharge of a spark between the terminals of the spark plug.

In testimony whereof I affix my signature.

RALPH E. HANTZSCH. 

